1. Technical Field
The present invention relates to disk drives in general, and in particular to a rotary actuator within disk drives. Still more particularly, the present invention relates to a low friction pivot for a rotary actuator within disk drives.
2. Description of the Prior Art
In the prior art, a rotary voice coil actuator within a disk drive typically employs an upper and a lower ball-bearing assemblies. Such assemblies manifest a frictional torque in accordance with the ball friction multiplied by a radius extending from the center of rotation of an actuator shaft to approximately the center of rotation of a nominal rotating ball of the bearing assembly. This type of rotary actuator design is relatively low cost and has experienced widespread usages.
However, when the storage density of disk drives becomes increasingly higher, the size of the actuator within these disk drives also needs to be smaller and smaller. As the actuator becomes smaller, the ratio of friction (both static and dynamic) to actuator inertia may increase to a point that it becomes very difficult for an actuator-head-positioning servo system to make small displacements that are required for single-track seeking and for following a data-storage track centerline. In addition, with the increase in track densities, it is tremendously difficult to provide a motion with ever decreasing magnitude to carry out small distance seeks and to maintain a desired head position over a track.
One of the many disadvantages of the ball bearing assembly design is that undesirable low frequency resonance incident to small motions of the ball bearings in actuators attributed to the distortions of the ball can cause high stiffness with very low damping. During small motions, the actuator ball responds to an applied force by deforming elastically. This driving force will be increased until the actuator ball starts to roll and motion is realized. Unfortunately, by the time the actuator ball is driven out of its stick/slip state and into rotary movement, excessive driving current has been applied, and the transducer head is significantly mispositioned with respect to the desired track position. Furthermore, any initial deformation of the actuator ball also results in high starting friction (or stiction). Consequently, it would be desirable to provide an improved pivot design for rotary actuators without utilizing ball bearings.